Revert "Fixing bug #3817."

This reverts commit ad2a0308b1592c7235714a2cca926f3b55accbb2.
Fixing bug #3858 and #3817 in one stroke.
Fix merging of name maps in union of universe contexts.
initial commit about coq2rust.  just compiles.
compiles and prints something, quite like Haskell.
definition of unit is now printed.
Tt can be printed.
files for testing rust extraction.
can print booleans.
can print empty inductive type.
add something in README
definition of inductive types with arguments to constructors.
prints an inhabitant of a singleton inductive.
print a term in inductive type with an argument.
print a term of inductive type with two arguments
put things in box and produce natural numbers.
fixed some mistakes.
can print a constant function.